The overall goal of the current studies is to determine mechanisms responsible for the gender differences in immune dysfunction that results from the combined insult of acute ethanol exposure and a 15% total body surface area dorsal scald injury. We previously reported that in the first 48 hours after injury, male mice given burn + ethanol had greater immune dysfunction (decreased delayed type hypersensitivity and splenocyte proliferative responses) than following either insult alone. This dysfunction was mediated by the overproduction of macrophage-derived proinflammatory cytokines, including interleukin-6 (IL-6), and could be restored by treatment with low physiologic levels of 17beta-estradiol (E2). Low levels of E2 mediate the well-documented gender difference in immunity, in which the immune system of healthy females is "stronger" than that of males. Surprisingly, we found that female mice subjected to burn injury were more immunosuppressed than male mice. As with female burn patients, burned female mice have a prolonged elevation in circulating E2 levels, which reaches pregnancy levels of the hormone, a concentration that enhances the production of IL-6 and suppresses immune responses. Males have a transient, more moderate rise in E2 along with a concomitant decrease in testosterone. In this proposal, we plan to compare immune responses in intact and gonadectomized mice of both genders and focus on how treatment with hormones and hormone receptor antagonists influences immunity after the combined insult. Mechanisms by which E2 controls the production of proinflammatory cytokines by macrophages obtained from male and female mice given ethanol and burn injury with and without hormone modulation will be explored. These studies will include examining 1) the levels of estrogen receptor (ER)alpha and beta and variant receptors, 2) transcription factors (including NF-kappaB), and 3) signaling pathways (mitogen activated protein (MAP) kinase) leading to the overproduction of IL-6, a cytokine thought to play a critical role in triggering post-burn immunosuppression. Taken together, these studies will define how gonadal steroid hormones modulate immune responses in male and female mice given ethanol before burn injury. Additionally, by comparing immune responses in intact and hormone manipulated male and female mice, we should be able to determine if the depressed immunity in female mice is due to 1) the presence of high levels of E2, 2) the lack of testosterone, or 3) a combination of both. Finally, these studies will confirm whether manipulating the hormone milieu can improve immune status of ethanol-exposed burn patients and whether gender-specific treatments should be implemented.